This project contributes directly to the field of clinical Dermatology. Mitotic stimulating effects of Actinomycin D, environmental heat, hormones and wounding will be analyzed in epidermis of mouse skin and in both normal and diseased human skin. We have formulated a general model which approaches the problem of the control of epidermal mitosis from the point of view of induction and superinduction on the level of gene expression. We have used this model to design experiments studying the effects of specific chemicals, high temperature and wounding on epidermal mitotic activity. Studies are performed both in vitro and in vivo using cytological and cytochemical methods. The effects of these various agents are studied in relation to the specific responses of the G1 and the G2-populations of epidermal cells.